The present invention relates to a supercharger device for supercharging an internal combustion engine to increase the output level thereof, and more particularly, to a supercharging device comprising a mechanical type supercharger of which the rotational frequency is regulated by a belt type continuously variable transmission which uses the centrifugal force of a flyweight provided therein.
A conventional mechanical type supercharger whose rotational frequency is controlled by a belt type continuously variable transmission (often abbreviated to CVT) which uses the centrifugal force of a flyweight provided therein has been disclosed in the official announcement Hei 3-500564 which is the Japanese translated one of the international publication No. W089/02521. In this supercharger, a runner shaft with a runner is rotatably supported inside a housing. In order to supercharge the internal combustion engine, the runner shaft is driven by a secondary pulley device (a driven pulley device) of the continuously variable transmission which is driven by the internal combustion engine through an electromagnetic clutch and a speed increasing gear device.
Although the above identified application does not disclose a primary pulley (a drive pulley) of a continuously variable transmission, a primary pulley as well as a secondary pulley in a continuously variable transmission is disclosed in Japanese Utility Model Application Laid Open (Prepublicatlon) No. 1-69400 (1989). In this transmission, the drive pulley and the driven pulley each comprise a mutually opposed fixed flange (disk) and a movable flange. The fixed flanges of the drive pulley and the driven pulley are arranged on relative opposite sides. The movable flanges serve to vary the widths of V-shaped grooves of the drive pulley and the driven pulley. A flyweight for generating a centrifugal force is provided in at least one of the drive pulley and the driven pulley. Also, a spring for generating a force against the centrifugal force is provided in at least one of the drive pulley and the driven pulley.
In the above-described supercharger, even when the engine speed varies, if the engine speed is within a predetermined range, the rotational frequency of the supercharger can be controlled by the continuously-variable transmission so as to be maintained substantially constant. Moreover, only under a heavy load condition which requires the supercharger to be operated, the supercharger is operated while receiving power transmitted through an electromagnetic clutch to improve engine performance, i.e., driving ability. Namely, once the engine speed reaches a certain level, the conventional mechanical type supercharger with the CVT of a centrifugal weight type is controlled so that the rotational frequency of the supercharger is maintained at a predetermined constant level, regardless of the load on the internal combustion engine.
However, because of the above described device, even under partial load conditions or relatively light load conditions which require no supercharging, the rotational frequency of the supercharger reaches the predetermined constant level, i.e., a high rotational frequency level, thereby causing inefficient fuel consumption.
Further, although the electromagnetic clutch is employed to cut off the power transmitted to the supercharger under the partial load condition, the driving ability is unfavorably affected by on/off operation of the electromagnetic clutch in response to the variation in the load, thereby causing poor driving conditions. Consequently, the cutoff range has to be narrow, thereby resulting in poor fuel consumption.